Bismuth-containing catalysts

Abstract

The active phase of a catalyst composition contains at least one bismuth oxide compound in which bismuth is present at least partly in oxidation state +5, the bismuth oxide compound furthermore containing at least one basic metal component stabilizing the oxidation state +5, and said catalyst composition is used in oxidation and dehydrogenation reactions under heterogeneous catalysis, in particular the preparation of chlorine from hydrogen chloride.

We claim:  
     
       1. A process for the preparation of chlorine by oxidation of hydrogen chloride, which comprises (a) bringing a catalyst composition into contact with hydrogen chloride, wherein the active phase of the catalyst composition contains at least one bismuth oxide compound in which bismuth is present at least partly in oxidation state +5 and the bismuth oxide compound further containing at least one basic metal component stabilizing the oxidation state +5, to oxidize the hydrogen chloride to chlorine and to cause a decrease in the oxidation state of the bismuth and (b) re-oxidizing the catalyst composition before the average oxidation state of the bismuth decreases to +3. 
     
     
       2. A process as claimed in claim  1 , wherein the amount of Bi +5 of the catalyst composition is from about 1 to 99% by weight, based on the total bismuth content. 
     
     
       3. A process as claimed in claim  1 , wherein the basic metal component of the catalyst composition is selected from the group consisting of alkali metal, alkaline earth metal and rare earth metal. 
     
     
       4. A process as claimed in claim  3 , wherein the basic metal component of the catalyst composition is selected from the group consisting of Li, Na, K, Sr, Ba, Cs, Y and La. 
     
     
       5. A process as claimed in claim  1 , wherein the active phase of the catalyst composition contains at least one compound of the formula: 
       
         
           KBi y O z    
         
       
       where 
       y is from 0.5 to 2 and  
       z is from 1.25 to 5.5,  
       or of the formula: 
       
         
           BaBi y O z    
         
       
       where 
       y is from 0.17 to 3 and  
       z is from 1.43 to 5.6,  
       in each case at least part of the Bi is present in oxidation state +5. 
     
     
       6. A process as claimed in claim  5 , wherein the active phase of the catalyst composition contains at least one compound of the formula KBi y O z , wherein the quotient y/z is from about 0.4 to about 0.36. 
     
     
       7. A process as claimed in claim  5 , wherein the active phase of the catalyst composition contains at least one compound of the formula BaBi y O z , wherein the quotient y/z is from about 0.12 to about 0.54. 
     
     
       8. A process as claimed in claim  1 , wherein the active phase of the catalyst composition furthermore contains at least one promoter selected from elements of main groups 1, 2 and 4 and from subgroup 4 and/or 6 of the Periodic Table. 
     
     
       9. A process as claimed in claim  1 , wherein the catalyst composition 
       a) is in the form of an unsupported catalyst;  
       b) has been mixed with a binder or  
       c) has been applied to an inert carrier.  
     
     
       10. A process as claimed in claim  1 , wherein the process is a steady state procedure, said hydrogen chloride together with an oxygen-containing gas are brought into contact with the catalyst composition and hydrogen chloride; oxidized to chlorine. 
     
     
       11. A process as claimed in claim  10 , wherein the catalyst composition is used as a fixed bed, fluidized bed, moving bed or fluid bed. 
     
     
       12. A process as claimed in claim  1 , wherein the process is a non-steady-state procedure, and in step a) the catalyst composition is brought into contact with an oxygen-free gas containing the hydrogen chloride, the hydrogen chloride is oxidized to chlorine and the reaction products are removed, and in step b), at least some of the total catalyst composition is reoxidized in the presence of an oxygen-containing gas. 
     
     
       13. A process as claimed in claim  12 , wherein the catalyst composition is used as a fluidized bed, moving bed or fluid bed.